Nitrogen oxide or ‘NOx’ adsorbers are used to remove nitrogen oxides from the exhaust streams of both mobile and stationary internal combustion engines. However, the efficiency of such NOx adsorbers is reduced in the presence of sulfur containing compounds. Such sulfur containing compounds, especially sulfur containing aromatic compounds, ‘poison’ or react ‘irreversibly’ with the catalysts of NOx adsorbers. NOx adsorbers having contaminated catalysts have reduced efficiency. As a result, the presence of sulfur containing compounds in fuels used in internal combustion engines can have a deleterious effect upon exhaust emissions, especially with respect to nitrous oxide emissions. This problem is of particular concern in motor vehicles and stationary systems employing diesel engines.
The catalysts in NOx adsorbers typically undergo regenerative processes designed to extend the life expectancy of the catalyst/NOx adsorber. A first type of regenerative process is designed to drive off the NOx in the form of nitrogen from the NOx adsorber. In a second type of regenerative process, contaminants such as sulfur containing compounds are released or removed. The later process is sometimes referred to as desulfation and typically occurs at higher temperatures then the NOx regeneration process. Repeated exposure to such high temperatures can adversely affect catalyst life expectancy.
The concentration of sulfur containing compounds present in the fuel stream directly impacts how often a NOx adsorber must undergo desulfation. The higher the concentration, the more often the catalyst of a NOx adsorber must undergo desulfation. Similarly, a NOx adsorber will have a shorter life expectancy the more often it undergoes desulfation.
It would thus be advantageous to provide a fuel filter capable of minimizing the adverse effect of sulfur contaminants on the NOX adsorber.
The prior art has attempted to provide devices that remove sulfur-containing fuels from internal combustion engine fuel streams. For example, U.S. Patent Application Publication No. U.S. 2002/0028505 A1, the contents of which are incorporated herein by reference thereto discloses a desulfation apparatus to be mounted in automobiles, which is arranged between a fuel tank and an injector of an engine, the apparatus comprising a combination of a sulfur-containing compound adsorbent for adsorbing and concentrating the sulfur-containing compound and a sulfur-containing compound oxidizing agent or oxidation catalyst for oxidizing the adsorbed sulfur-containing compound, the apparatus further comprising a means for recovering and removing the resulting sulfur-containing oxide.
However, there remains a need for devices, especially fuel filters, that could reduce the amount of sulfur containing compounds in an internal combustion fuel stream to a desirable concentration, especially to concentrations of 3 ppm or less.
It would also be advantageous if such a fuel filter could be regenerated, that is, could distribute some or all of the stored sulfur containing compounds in order to extend the life cycle or capacity of the fuel filter. It would be particularly advantageous if such regeneration could occur without imposing a deleterious effect upon the NOx adsorber or upon engine exhaust emissions. It would also be desirable if such a fuel filter could thus extend the life cycle of NOx adsorbers by reducing the frequency of desulfation.